Control method for hydraulic type continuously variable transmission

Abstract

A control method for a hydraulic type continuously variable transmission for suppressing a harmful effect due to the reacceleration just after deceleration of a vehicle. In a hydraulic type continuously variable transmission, the operation of a shifting actuator is stopped to suspend the shift control (S 7 ) when a throttle valve is rapidly opened just after fully closed (S 4 : Yes) and an engine speed NE [rpm] is being rapidly increased (S 6 : Yes). Accordingly, even when the actual engine speed NE becomes much greater than a target engine speed T_NE during reacceleration just after deceleration of a vehicle, unexpected shift control (upshifting) can be prevented, so that more desirable torque can be produced.

1. A control method for a hydraulic type continuously variable transmission having
 a hydraulic pump adapted to be rotationally driven by a drive source, 
 a hydraulic motor adapted to be rotationally driven by an oil pressure generated by said hydraulic pump, and 
 a hydraulic circuit having:
 a high-pressure oil passage for feeding a working fluid from said hydraulic pump to said hydraulic motor, and 
 a low-pressure oil passage for feeding said working fluid from said hydraulic motor to said hydraulic pump, said control method comprising the steps of: 
 
 determining whether or not a reaccelerating operation just after a decelerating operation is performed in said hydraulic type continuously variable transmission; and 
 correcting for an alienation between an actual output and a target output from said hydraulic motor due to the pressure difference between said high-pressure oil passage and said low-pressure oil passage when said reaccelerating operation is performed. 
 
     
     
       2. The control method for the hydraulic type continuously variable transmission according to  claim 1 , wherein:
 said drive source comprises an engine; 
 said determining step is performed according to a rate of increase in throttle angle and a rate of increase in engine speed; and 
 said correcting step is performed by suspending shift control in said hydraulic type continuously variable transmission when said reaccelerating operation is performed. 
 
     
     
       3. The control method for the hydraulic type continuously variable transmission according to  claim 2 , wherein said shift control is resumed according to a decrease in the rate of increase in said engine speed. 
     
     
       4. The control method for the hydraulic type continuously variable transmission according to  claim 2 , wherein said shift control is resumed when said engine speed is lowered to a target value. 
     
     
       5. The control method for the hydraulic type continuously variable transmission according to  claim 3 , wherein said shift control is resumed when said engine speed is lowered to a target value. 
     
     
       6. The control method for the hydraulic type continuously variable transmission according to  claim 1 , wherein an electrical control unit is operatively connected to a shifting actuator for controlling an angle of inclination of a motor swash plate. 
     
     
       7. The control method for the hydraulic type continuously variable transmission according to  claim 6 , wherein the electrical control unit controls a speed ratio according to a difference between an actual engine speed and a target engine speed wherein when the actual engine speed is lower than the target engine speed, the electrical control unit decreases the speed ratio and wherein when the actual engine speed is higher than the target engine speed, the electrical control unit increases the speed ratio. 
     
     
       8. The control method for the hydraulic type continuously variable transmission according to  claim 6 , wherein when it is determined that reaccelerating is occurring just after deceleration, the shifting actuator is driven to temporarily move the motor swash plate in the vertical direction for correcting for the alienation. 
     
     
       9. The control method for the hydraulic type continuously variable transmission according to  claim 8 , wherein a new target engine speed may be temporarily set by subtracting a predetermined value from the target engine speed for correcting the alienation by using the new target engine speed. 
     
     
       10. The control method for the hydraulic type continuously variable transmission according to  claim 1 , wherein the deceleration and reacceleration is determined by a rate of change in a vehicle speed or the rate of change in a rotational speed of an output shaft of the hydraulic pump. 
     
     
       11. A control method for a hydraulic type continuously variable transmission comprising the following steps:
 rotationally driving a hydraulic pump by a drive source, 
 rotationally driving a hydraulic motor by an oil pressure generated by said hydraulic pump, and 
 providing a hydraulic circuit including:
 feeding a working fluid through a high-pressure oil passage from said hydraulic pump to said hydraulic motor, and 
 feeding the working fluid through a low-pressure oil passage from said hydraulic motor to said hydraulic pump; 
 
 determining whether or not a reaccelerating operation just after a decelerating operation is performed in said hydraulic type continuously variable transmission; and 
 correcting for an alienation between an actual output and a target output from said hydraulic motor due to the pressure difference between said high-pressure oil passage and said low-pressure oil passage when said reaccelerating operation is performed. 
 
     
     
       12. The control method for the hydraulic type continuously variable transmission according to  claim 11 , wherein:
 said drive source comprises an engine; 
 said determining step is performed according to a rate of increase in throttle angle and a rate of increase in engine speed; and 
 said correcting step is performed by suspending shift control in said hydraulic type continuously variable transmission when said reaccelerating operation is performed. 
 
     
     
       13. The control method for the hydraulic type continuously variable transmission according to  claim 12 , wherein said shift control is resumed according to a decrease in the rate of increase in said engine speed. 
     
     
       14. The control method for the hydraulic type continuously variable transmission according to  claim 12 , wherein said shift control is resumed when said engine speed is lowered to a target value. 
     
     
       15. The control method for the hydraulic type continuously variable transmission according to  claim 13 , wherein said shift control is resumed when said engine speed is lowered to a target value. 
     
     
       16. The control method for the hydraulic type continuously variable transmission according to  claim 11 , wherein an electrical control unit is operatively connected to a shifting actuator for controlling an angle of inclination of a motor swash plate. 
     
     
       17. The control method for the hydraulic type continuously variable transmission according to  claim 16 , wherein the electrical control unit controls a speed ratio according to a difference between an actual engine speed and a target engine speed wherein when the actual engine speed is lower than the target engine speed, the electrical control unit decreases the speed ratio and wherein when the actual engine speed is higher than the target engine speed, the electrical control unit increases the speed ratio. 
     
     
       18. The control method for the hydraulic type continuously variable transmission according to  claim 16 , wherein when it is determined that reaccelerating is occurring just after deceleration, the shifting actuator is driven to temporarily move the motor swash plate in the vertical direction for correcting for the alienation. 
     
     
       19. The control method for the hydraulic type continuously variable transmission according to  claim 18 , wherein a new target engine speed may be temporarily set by subtracting a predetermined value from the target engine speed for correcting the alienation by using the new target engine speed. 
     
     
       20. The control method for the hydraulic type continuously variable transmission according to  claim 11 , wherein the deceleration and reacceleration is determined by a rate of change in a vehicle speed or the rate of change in a rotational speed of an output shaft of the hydraulic pump.